Passive throttling valve outside of muffler

ABSTRACT

An exhaust system includes an exhaust tube for conveying a heated exhaust flow from an engine. A valve is mounted at least partially within the exhaust tube for noise attenuation. The valve includes a bias member mounted outside of the engine exhaust tube within a heat transfer environment to maintain the bias member at a low temperature. The bias member biases the valve against the heat exhaust flow toward a predetermined position. The valve is mounted within a section of the tube having a smaller cross-sectional area and pivots into a larger cross-sectional area section of the exhaust tube to avoid interference with tube walls and provide a relatively large range of movement.

BACKGROUND OF THE INVENTION

This invention relates to vehicle exhaust systems and, more particularly, to a passive noise attenuation valve for use with an exhaust tube of the vehicle exhaust system.

Exhaust systems are widely known and used with combustion engines. Typically, the exhaust system includes exhaust tubes that convey hot exhaust gases from the engine to a muffler. The muffler includes acoustic chambers that cancel out sound waves carried by the exhaust gases. Although effective, mufflers are often relatively large in size and provide limited nose attenuation.

It has been proposed to utilize a valve within the exhaust tubes to provide noise attenuation. However, the proposed valves have numerous drawbacks that limit widespread use. For example, the temperature of the hot exhaust gas is approximately 1000° C., and therefore the valve requires actuation mechanisms that utilize special materials, that are relatively expensive, to withstand the severe temperatures. Moreover, since the valves are located within the exhaust tubes, they obstruct the flow of the exhaust gases and thereby limit effectiveness of the valve for noise attenuation. Therefore, there is a need for a more effective noise attenuation valve that additionally improves exhaust flow. This invention addresses those needs while avoiding the shortcomings and drawbacks of the prior art.

SUMMARY OF THE INVENTION

In one aspect, an exhaust system includes an exhaust tube for conveying a heated exhaust flow from an engine. A valve is mounted at least partially within the exhaust tube for noise attenuation. The valve includes a biasing member mounted outside of the engine exhaust tube within a heat transfer environment to maintain the biasing member at a low temperature. The biasing member biases the valve against the heated exhaust flow toward a predetermined position.

In one particular example, the valve is mounted within a section of the exhaust tube having a reduced cross-sectional area and is pivotable into a larger cross-sectional area section of the exhaust tube to avoid interference with tube walls and provide a relatively large range of movement.

In another example, the valve includes a four-bar linkage that connects a valve plate of the valve to the biasing member. The four-bar linkage varies an amount of force necessary to compress the biasing member. In one example, the biasing member s a spring, and the four-bar linkage varies a spring constant of the spring at different rotational positions of the valve plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.

FIG. 1 is a schematic view of an example exhaust system.

FIG. 2A is a perspective view of an example noise attenuation device for use in the exhaust system.

FIG. 2B is a perspective view of an example valve within the noise attenuation device.

FIG. 3 is a perspective view of an example exhaust tube for mounting the valve.

FIG. 4 is a perspective view of an example noise attenuation device having a valve plate in an open position.

FIG. 5 is a schematic view of an example linkage for obtaining a variable spring constant within an example valve.

FIG. 6 is a schematic view of the example linkage of FIG. 5 in a rotated position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically illustrates selected portions of an example exhaust system 20. In this example, the exhaust system 20 includes an engine 22, such as a gas combustion engine for use in a vehicle. The engine 22 is connected to one or more exhaust tubes 24 for conveying hot exhaust gases from the engine 22 to a muffler 26. A noise attenuation device 28 is associated with the exhaust tube 24 for reducing sound carried by the exhaust gases. Although, the illustrated example includes the muffler 26, the noise attenuation device 28 can be used without the muffler 26, or instead of the muffler 26.

FIG. 2A illustrates a perspective view of one example noise attenuation device 28. In this example, the noise attenuation device 28 includes an exhaust tube section 40 connected to the exhaust tube 24 from the engine 22 for conveying the heated exhaust gases. A valve 42 is disposed at least partially within the exhaust tube section 40 to attenuate noise carried by the exhaust gases.

In one example, the engine 22 produces pressure pulses, or acoustic waves, associated with combustion cycles of firing one or more pistons. Noise is caused by the release of the pressure pulses. The valve 42 of the noise attenuation device 28 reduces the noise by reflection. The acoustic waves are reflected back and forth within the exhaust system 20. At each reflection, the sound waves lose energy. As result, only a fraction of the noise leaves the exhaust system 20.

Referring to an isolated view of the valve 42 in FIG. 2B, the valve 42 includes a valve plate 44 connected to a pivot shaft 46. The pivot shaft 46 extends through a frame 48, which supports bushings 50 for pivotally supporting the pivot shaft 46. In this example, a threaded member 52 is secured over an end of the pivot shaft 46 that extends from the frame 48. A bias member 54, a spring in this example, is received over the threaded member 52 and the end of the pivot shaft 46 (for convenience of showing the threaded member 52, the bias member 54 is not shown assembled in FIG. 2B). Alternatively, the end of the pivot shaft 46 is threaded instead of using the threaded member 52.

The bias member 54 includes a first extended portion 56 a that abuts a first arm 58 a that extends from the frame 48. A second extended portion 56 b extends from the other end of the bias member 54 and abuts a second arm 58 b that extends from a fastener 60 that is received onto the threaded member 52.

In the illustrated example, the valve plate 44 extends into the exhaust tube section 40 (FIG. 2A). In this example, the valve plate 44 is contoured in an airfoil shape, to reduce resistance of exhaust gas flow over a surface of the valve plate 44.

Referring to FIG. 3, the exhaust tube section 40 includes a first section 70 a and a second section 70 b. In this example, the first section 70 a and second section 70 b are generally round in cross-section. The first section 70 a includes a first cross-sectional area associated with a diameter D₁ of the first section 70 a. The second section 70 b includes a second cross-sectional area associated with the diameter D₂ of the second section 70 b. In this example, the cross-sectional area of the second section 70 b is larger than the cross-sectional area of the first section 70 a.

The first section 70 a includes a slot 72 for mounting the valve 42. The slot 72 is near a transition section 74 between the first section 70 a and the second section 70 b. The slot 72 includes notches 76 at each corner of the slot 72 for receiving corresponding portions of the frame 48. In this example, the frame 48 fits within the notches 76 to secure the valve 42 in place. Optionally, the frame 48 is welded or secured in another known manner to the exhaust tube section 40 to lock the valve 42 in place. Alternatively, the valve 42 is mounted to walls of the exhaust tube section 40 in a known manner without the slot 72. In one example, the valve 42 is mounted within the first section 70 a of the exhaust tube section 40 before the first section 70 a is secured to the second section 70 b. In another example, the first section 70 a is formed, such as by stamping, with a suitable mounting portion for attaching the valve 42. Given this description, one of ordinary skill in the art will recognize other suitable designs for mounting the valve 42.

In this disclosed example, the bias member 54 biases the valve plate 44 toward a predetermined, minimum flow position, such as the position shown in FIG. 2A, wherein the valve plate 44 is generally perpendicular to the flow of exhaust gases through the exhaust tube section 40. In the disclosed example, the valve plate 44 is smaller than a cross-section of the exhaust tube section 40 such that in the minimum flow position, the valve plate 44 permits the hot exhaust gases to flow through the exhaust tube section 40.

The bias member 54 is located outside of the exhaust tube section 40. In this example, the bias member 54 is within a heat transfer environment H that removes heat to maintain the bias member 54 below a threshold temperature. For example, the exhaust gas conveyed through the exhaust tube section 40 is approximately 1000° C. A portion of the heat from the exhaust gas is transferred through the valve plate 44 to the bias member 54. In this example, the heat transfer environment H provides a surrounding ambient airflow that removes and transfers the heat away to maintain the bias member 54 at a lower temperature than the exhaust gas. In one example, the lower temperature permits the bias member 54 to be made from standard types of materials rather than expensive, specialized materials for withstanding elevated temperatures. In one example, the heat transfer environment H is a relatively uncontained volume around the exhaust tube section 40, such as an ambient airflow adjacent an undercarriage of a vehicle.

Operationally, the valve 42 functions as a passive throttle within the exhaust tube 24 to attenuate acoustic waves carried by the exhaust gases. The valve plate 44 reflects a portion of the acoustic waves to attenuate noise as described above. The valve plate 44 pivots with the pivot shaft 46 about an axis A in response to a force exerted on a valve plate 44 from the flow of the exhaust gas. The valve plate 44 pivots between the minimum flow position and a maximum flow position (FIG. 4) wherein the valve plate 44 is oriented about 90° relative to the minimum flow position to permit the exhaust gas to flow through the exhaust tube 24.

Rotation of the pivot shaft 46 causes the threaded member 52 and fastener 60 to also rotate. Rotation of the fastener 60 moves the second arm 58 b against the second extended portion 56 b of the bias member 54. The first extended portion 56 a of the bias member 54 presses against the first arm 58 a and provides resistance to rotation. Thus, movement of the valve plate 44 acts against the biasing force provided by the bias member 54.

The flow of exhaust gases tends to move the valve plate 44 from the minimum flow position shown in FIG. 2 toward the maximum flow position shown in FIG. 4. The difference in the cross-sectional areas of the first section 70 a and a second section 70 b of the exhaust tube section 40 permits the valve plate 44 to move to the maximum flow position without interfering with walls of the second section 70 b. In the minimum flow position, the valve plate 44 is entirely within the first section 70 a. When the valve plate 44 pivots from the minimum flow position to the maximum flow position, the valve plate 44 pivots into the second section 70 b. In the maximum flow position, the valve plate 44 is almost entirely out of the flow path of the exhaust gases, approximately 90° from perpendicular. The unobstructed movement of the valve plate 44 and pivoting the valve plate 44 about axis A near a perimeter of the exhaust tube section 40 (e.g., rather than about a central pivot through the valve plate 44) provides the benefit of minimizing obstruction of the exhaust gases through the exhaust tube section 40. Additionally, as can be appreciated from the above description, the valve 42 has relatively few moving parts, which enhances durability of the valve 42.

FIG. 5 shows a schematic view of an alternative bias member 54. In this example, the arrangement includes a linkage 86, such as a type of linkage commonly known in kinematics as a four-bar linkage, that connects a valve plate 44′ to the bias member 54′. The valve plate 44′ is pivotally connected about axis 0 to a first link 88 a. A second link 88 b includes one end that is pivotally secured for rotation about a pivot shaft 46′, which is concentric with the bias member 54′ similar to as described above, such that rotation of the pivot shaft 46′ compresses the bias member 54′. A third link 88 c is pivotally connected with the other ends of the first link 88 a and the second link 88 b.

Operationally, the first link 88 a pivots with movement of the valve plate 44′ due to the force of the exhaust gas. Movement of the first link 88 a moves the third link 88 c, which in turn rotates the second link 88 b against the bias force of the bias member 54′.

In this example, the bias member 54′ includes a spring having a spring constant associated with the amount of force necessary to compress the bias member 54′ a given amount. In the position shown in FIG. 5, a relatively large amount of force is necessary to move the valve plate 44′ against the bias force of the bias member 54′. However, as shown in FIG. 6, as the first link 88 a and the second link 88 b rotate counterclockwise in response to the force of the exhaust gases, less force is needed to move the first link 88 a against the biasing force of the bias member 54′.

The amount of force and the spring constant can be determined in a known manner at various rotational positions of the valve plate 44′ and depends on the length of the links 88 a, 88 b, and 88 c, angles between the links 88 a, 88 b, and 88 c, angular velocity, angular acceleration, and inertia of a given example. As a result of the varying amount of force required to pivot the valve plate 44′, the spring constant is effectively changed over the rotation of the valve plate 44′. Varying the effective spring constant provides the benefit of tailoring the response of the valve 42 in a desired manner over the rotational position of the valve plate 44′ based upon an expected exhaust gas flow.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention. 

1. An exhaust system comprising: an exhaust tube for conveying a heated exhaust flow; a valve disposed at least partially within the exhaust tube; and a bias member mounted outside of the exhaust tube, the bias member biasing the valve against the heated exhaust flow toward a predetermined position.
 2. The exhaust system as recited in claim 1, wherein the bias member is mounted within an ambient airflow heat transfer environment that removes heat from the bias member to maintain the bias member at a temperature below a threshold temperature.
 3. The exhaust system as recited in claim 1, wherein the valve includes a valve plate coupled to the bias member, and wherein the exhaust tube includes a tube wall having a slot therein, and the valve is mounted within the slot such that the valve plate is within the exhaust tube.
 4. The exhaust system as recited in claim 1, wherein the valve is moveable between a plurality of positions including the predetermined position, and the bias member comprises a spring rate that varies between the plurality of positions.
 5. The exhaust system as recited in claim 1, wherein the exhaust tube includes a first section having a first cross-sectional area adjacent a second section having a second cross-sectional area that is larger than the first cross-sectional area.
 6. The exhaust system as recited in claim 5, wherein the valve includes a valve plate that is mounted at least partially within the first section and is pivotable between a plurality of positions, and in at least one of the plurality of positions, the valve plate pivots into the second section.
 7. The exhaust system as recited in claim 1, wherein the valve includes a valve plate within the exhaust tube that is pivotable between a minimum flow position and a maximum flow position, wherein the valve plate permits the heated exhaust flow through the exhaust tube in each of the minimum flow position and the maximum flow position.
 8. The exhaust system as recited in claim 1, wherein the valve includes a valve plate within the exhaust tube that is pivotable about a pivot axis that is located at an outer perimeter of the valve plate.
 9. The exhaust system as recited in claim 1, wherein the valve includes a linkage connecting the valve and the bias member, the linkage comprising a first link having one end pivotally secured for rotation about a pivot axis of the valve, a second link having an end pivotally secured for rotation about a pivot axis of the bias member, and a third link that connects another end of the first link to another end of the second link.
 10. The exhaust system as recited in claim 9, wherein the first link comprises a first nominal length, and the second link comprises a second nominal length that is longer than the first nominal length.
 11. An exhaust system comprising: an exhaust tube for conveying a heated exhaust flow, the exhaust tube comprising a first section having a first cross-sectional area adjacent a second section having a second cross-sectional area that is larger than the first cross-sectional area; a valve mounted at least partially within the first section, the valve operative to move between a plurality of positions in response to a force exerted on the valve from the heated exhaust flow, and wherein in one of the plurality of positions, the valve extends into the second section.
 12. The exhaust system as recited in claim 11, further comprising a bias member that biases the valve toward a predetermined position among the plurality of positions.
 13. The exhaust system as recited in claim 12, wherein the plurality of positions includes a minimum flow position where the valve is generally perpendicular to a direction of the heated exhaust gas flow through the exhaust tube, and a maximum flow position where the valve is oriented 90° relative to the valve in the minimum flow position.
 14. The exhaust system as recited in claim 13, wherein the predetermined position comprises the minimum flow position.
 15. The exhaust system as recited in claim 12, wherein the bias member comprises a spring having a spring rate that varies between the plurality of positions.
 16. The exhaust system as recited in claim 11, wherein the valve includes a pivot shaft having a pivot axis, and a valve plate coupled to the pivot shaft for movement about the pivot axis, wherein the valve plate is at least partially within the exhaust tube.
 17. The exhaust system as recited in claim 16, wherein the pivot shaft is entirely outside of the exhaust tube.
 18. A method of controlling a valve for use in an exhaust system, comprising the steps of: mounting the valve within a first section of an exhaust tube, the first section having a first cross-sectional area; and moving the valve such that the valve extends at least partially into a second section of the exhaust tube having a second cross-sectional area that is larger than the first cross-sectional area to avoid interference between the valve and the second section.
 19. The method recited in claim 18, further including biasing the valve toward a predetermined position that is about perpendicular to a direction of an exhaust gas flow through the first section.
 20. The method recited in claim 19, further including passively moving the valve with a force provided by the exhaust flow to an orientation that is about 90° relative to the valve predetermined position such that the valve extends into the second section.
 21. The method recited in claim 18, further including mounting a bias member of the valve outside of the exhaust tube in an air flow to maintain a temperature of the bias member below a temperature of an exhaust gas flow through the exhaust tube. 